


Uncle Arthur

by platonic_boner



Category: Merlin (TV)
Genre: Age Regression/De-Aging, Canon Era, Fluff, Kid Fic, M/M, Magic Revealed
Language: English
Status: Completed
Published: 2016-02-25
Updated: 2016-02-25
Packaged: 2018-05-23 06:02:32
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,597
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6107329
Author URL: https://archiveofourown.org/users/platonic_boner/pseuds/platonic_boner
Summary: <blockquote class="userstuff">
              <p>Merlin saves the day as Dragoon, but then botches the potion to turn himself young again. </p>
<p>Meanwhile, Arthur makes a new friend: a five-year-old named Marlin.</p>
            </blockquote>





	Uncle Arthur

**prologue**

Another day and another threat to Camelot and King Arthur extinguished. Merlin hurries back into Gaius’ rooms as fast as his old knees will allow, his long red robes swishing against the floor.

“Merlin!” Gaius exclaims, sounding insultingly surprised. “You’re back!”

“I _told_ you it would be fine,” Merlin says. Gaius had been very against Merlin’s plan, to the extent that he tried to stop Merlin by refusing to make the de-aging potion. Merlin had pointed out that he was perfectly capable of making potions by himself, and he’d done so - very handily, if he does say so himself.

He grabs the potion vial now and downs it, feeling very triumphant.

The feeling quite disappears when he starts shrinking.

“You idiot,” Gaius says, which is probably fair.

 

**day one**

Arthur’s good-for-nothing servant is missing, _again_. Arthur hasn’t seen him in almost a full day. He had to get dressed himself and find another servant to fetch his breakfast, and he is _not_ pleased. So he bursts into Gaius’ quarters, intent on demanding to know where Merlin is. Then he freezes.

Sitting across from Gaius at the table is a small child of perhaps five years old. Arthur has never seen this boy before, but it’s very clear to him who - or, rather, _whose_ \- he is by the ears alone.

“Merlin has a _son_?”

Arthur would normally make a joke about whether the mother was blind or something, but for one thing, he feels it would be tasteless to say that in front of the child, and besides, Merlin is nowhere to be seen, so insulting him isn’t as fun. Also, Arthur is too blindsided to think of it, and once he has, he’s realized, _Merlin has a child and I didn’t know_ , and he doesn’t feel like making jokes at all.

Gaius and the boy both look up at him in surprise.

“Uh… yes, sire,” Gaius says. “It’s … news to us as well.”

“Ah,” Arthur says, and the pit that had been opening up in his stomach at the thought that Merlin would keep a secret like this from him closes off abruptly.

Arthur examines the boy closely for a moment, curious. He’s the spitting image of Merlin, skinny with dark curls and sharp cheekbones and huge ears. In fact, the ears look bigger on this tiny child. He’s dressed in very old clothes, but he’s wearing a scarf around his neck that Arthur recognizes as one of Merlin’s. And he returns Arthur’s gaze head-on, just like Merlin does, as though Arthur is a normal person rather than the king of Camelot.

Arthur smiles. “What’s his name?”

“Uh… Marlin, sire,” Gaius says.

The boy makes a bit of a protesting noise and opens his mouth, but Gaius nudges him and whispers something insistently and he goes quiet. Arthur passes it off as nothing but Merlin’s son probably being as insolent as Merlin. Speaking of which...

“And where is Merlin?”

“Uh...he’s with the mother. She’s taken ill,” Gaius explains. “So she sent… Marlin here, and Merlin went to see if he could help.”

“I see,” Arthur says. He notes that Gaius looks somewhat annoyed. Probably, babysitting a five year old is not what a man of Gaius’ age wants to do. Arthur should definitely take Marlin off his hands; Gaius will undoubtedly be grateful.

Arthur walks over. “Hello, Marlin,” he says.

“Who’re you?” Marlin demands.

Arthur grins at him. “I’m Arthur. I’m your dad’s… You can just call me Arthur. Or, um,” he looks at Gaius and reddens, but continues, “or Uncle Arthur.”

Marlin sticks out a tiny hand and Arthur shakes it solemnly.

Arthur turns to Gaius. “I’ll take him off your hands,” he offers.

Gaius objects, but Arthur knows better. Gaius must be incredibly busy since he sent Merlin to deal with Marlin’s mother’s illness instead of going himself. Gaius is also clearly not suited to take care of a child all day - Marlin will have far more fun with Arthur. Gaius is probably just objecting because he thinks Arthur is too busy with kingly duties to babysit, but for Merlin’s child, Arthur will _make_ time.

“I’ll bring him back tonight!” Arthur scoops Marlin up and waves as they leave Gaius’ quarters.

*****

Arthur spends the entire day playing with Marlin. As Arthur knows from his own childhood, the castle is an amazing place for hide and seek, which they play for hours. It’s also fun to sneak into the kitchens and steal bits of food, which they do even though Arthur is king and could just order whatever he wanted. The stealing makes it taste better. After that they go play with the animals - the cats _hate_ Marlin but the dogs love him, and he loves the horses even though Arthur quickly decides they’re far too large to be trusted around such a small boy.

By the end of the day, Arthur feels slightly guilty. He isn't sure when Marlin's bedtime should be, but he knows it's passed them by already. Also, he probably should have made Marlin take a nap at some point. Marlin's been incredibly cranky for the last several hours, which Arthur has finally realized is probably connected to Marlin’s increasingly frequent, incredibly huge (and kind of adorable) yawns.

“Let’s get you to bed, huh?” Arthur says.

Arthur picks him up and carries him to Gaius' chambers. Halfway there, he feels Marlin’s head fall limply on his shoulder, and he realizes the boy is already sleeping. Arthur is a horrible caregiver.

Gaius is waiting up and gives Arthur the evil eyebrow when he enters, but doesn't say anything when he sees Marlin is asleep. Arthur takes Marlin to Merlin's room and sets him on the bed. Marlin only partly wakes up, so Arthur takes the boy's shoes off himself. He pulls back the covers, sets Marlin down, and pulls the covers over him. It feels weird to just turn and leave. Arthur hesitates.

"G'night, Arthur," Marlin mumbles.

"Goodnight," Arthur says, tucking the covers more securely around Marlin's shoulders.

On his way out, Gaius clears his throat. Arthur turns to look.

“Are you going to take him again tomorrow?”

“Yes,” Arthur says immediately.

"You'd better bring him back earlier. His bedtime is seven o'clock."

“I will,” Arthur says. “I’m sorry.”

Gaius nods approvingly. “We’ll see you tomorrow.”

 

**day two**

Arthur fetches Marlin after breakfast. He neglected all of his duties yesterday, which has made a number of people very unhappy with him, so he knows he can’t do the same thing today. Instead, he takes Marlin to the practice courts and sets him down in the grass a safe distance away.

"You can watch me training the knights," he explains. "Sit here and don't come any closer. Our swords are blunt but they could still hurt you."

Marlin nods and settles down.

Gwaine and Percival converge on Arthur as soon as he leaves Marlin’s side. They’re both grinning madly and refuse to let Arthur pass before he answers their questions.

“Who’s the child?” Percival asks.

“Is he yours?” Gwaine demands.

“Do you really think I would father a child with ears like that?” Arthur demands.

Both knights turn to look more closely at Marlin.

“It’s Merlin’s kid,” Percival concludes, holding out a hand palm-up. “Pay up, Gwaine.”

“That doesn’t prove me wrong!” Gwaine insists. “I can think of at least two scenarios in which Arthur could have fathered Merlin’s son.”

Arthur rolls his eyes and pushes past his knights. “Percival, please explain how children are made to Gwaine,” he calls over his shoulder. He doesn’t wait for an answer before calling the rest of the knights over and explaining what drills they will work on today.

*****

Half an hour into training, Arthur looks over to Marlin to check on him, but he isn’t where Arthur left him. Arthur has a brief moment of pure panic - he should’ve paid more attention to the child, should’ve checked on him more often, maybe he should’ve put a guard on him - and then he spots Percival.

Percival’s playing with the boy. He’s throwing Marlin in the air and catching him, and Marlin is giggling with delight. As Arthur watches, Percival holds the boy over his head and runs with him, and Marlin is screaming with laughter.

Arthur stomps over. It’s entirely because Percival is supposed to be training. It’s not at all because of how terrified Arthur just was when he couldn’t find Marlin for a few seconds, and it’s _absolutely_ not because Arthur is _jealous_ that Marlin’s having so much fun with someone else.

"Percival! Why aren't you training?" Arthur barks.

Percival sets the giggling boy down. "He was bored! I'm being careful."

"Arthur!" Marlin says, running to him. He says in a whisper, "Percy is _huge_ , is he part giant?"

Arthur lets out a strangled laugh. Percival himself snorts, clearly having overheard the whisper.

"I'll play with you after training is done, okay?" Arthur promises. "I have a surprise for you.”

This was perhaps the wrong thing to say, because Marlin starts practically bouncing with delight. “What is it, what is it?” he demands.

“I can’t tell you, it’s a surprise,” Arthur replies. He takes Marlin by the hand and pulls him back over to the patch of grass where Arthur had originally set him down. “Now, stay here and watch until I’m done training, and then we’ll go see your surprise, all right?”

Marlin immediately sits, staring up at Arthur with big excited eyes. Arthur grins. Marlin is awesome.

*****

The surprise is that Arthur has had the servants dig up all of Arthur’s childhood clothes, books, and most importantly, toys. They would never fit in Merlin’s room, so Arthur had the servants bring them to his own chambers, and he takes Marlin there now.

Marlin’s eyes grow wide at the sight of all the toys.

“Whose room is this?” he asks, cautiously.

“Mine,” Arthur says. “And these are all my old toys - but they’re yours now.”

Marlin squeals with delight, hugs Arthur around the legs, and then runs to rock on the hobby horse. As soon as he gets there, however, he spots Arthur’s toy soldiers in their fort, and he runs across the room to play with them. Then he has to play with the brightly coloured building blocks, and so on. Arthur just watches, grinning - except for when Marlin mistakes Arthur’s sword for a toy, and Arthur leaps towards him and snatches the sword away before Marlin can play with it. He has to quickly point the disappointed boy towards another shiny toy to stop him from crying.

Finally, Marlin settles on playing with the toy soldiers and insists that Arthur come be the evil teddy bear.

(“No, Marlin, this is the evil warlock,” Arthur tries, holding up the wooden, black-robed figure.

Marlin snatches it away from him and sets it beside the throne. “No, the warlock is friends with the king!”

Arthur figures when Marlin’s already got talking animals and women as knights, a sorcerer at the king’s right hand can’t hurt.)

Arthur takes Marlin back to Gaius immediately after dinner, then returns to his chambers. They seem very quiet and empty without Marlin - as well as an enormous mess. Arthur could call a maid to pick up the toys, but instead he does it himself, smiling the whole while as he remembers Marlin’s reactions to each toy.

 

**day three**

The next morning, Leon and Gwen accost Arthur and Marlin on their way to the stables. Arthur has fetched a basket of food for them from the kitchens, and asked for a pony to be saddled for Marlin. They’re going to have a _great time_ \- or, they would have, if only Marlin had obeyed his order to hide from Leon quickly enough.

“Sire,” Leon says, “There are important matters you need to attend to.”

“I’ve promised Marlin a picnic,” Arthur objects, holding up the basket as proof.

Gwen takes that as an opportunity to snatch the basket away from him. “And I’m sure we’ll have a good time, won’t we, Marlin? I’m Auntie Gwen,” she adds.

“Say goodbye to your Uncle Arthur, Marlin,” Leon says, as he grabs Arthur’s arm firmly and starts pulling Arthur away.

“Goodbye, Uncle Arthur!” Marlin says, waving with the hand Gwen isn’t holding.

“Bye, Marlin,” Arthur replies. “Have fun with Gwen!” he adds, sending a glare to Guinevere when Marlin isn’t looking. She shrugs.

Leon half-leads, half-drags Arthur to the throne room, where the knights and lords are sitting around the round table. “Sorry, sire,” Leon says (none too convincingly) as he shoves Arthur inside.

The only consolation in the fact that Arthur has to sit through the world’s longest and most boring council meeting is that Leon, the evil traitor, has to sit through it as well. Three hours in, it’s very clear that Leon regrets all of his recent life choices, which makes Arthur feel a bit better.

When the meeting finally ends, Gwen and Marlin are waiting outside the room. They look rather different than the last time Arthur saw them. That is, they are both wearing flower crowns. Gwen’s is tasteful and pretty. Marlin’s is … Arthur’s going to go with “enthusiastic”.

“Whose idea was this?” Gwaine crows.

“Mine!” Marlin exclaims. “Do you like it?”

The knights all fall over themselves to assure Marlin that he looks magnificent. Arthur calls him adorable and he pouts all through dinner and bedtime until Arthur finally switches it to “princely”. (Which is a complete and total lie.)

 

**day four**

Gwaine is the one to steal Marlin the next day, after Leon drags Arthur to do his job once again. Arthur had been disappointed, but not worried, when Gwen took Marlin away, but he’s concerned by the devilish grin Gwaine gives him as he scoops Marlin up and says, “Today I’m going to teach you what fun is, mini-Merlin!”

“Gwaine, I’m warning you,” Arthur begins, but he’s tugged away by Leon before he can finish the sentence. He thinks he got his point across anyways, but he knows Gwaine isn’t likely to listen regardless.

Gwaine’s adventures in babysitting end with Marlin being lost for more than an hour after Gwaine proposes a city-wide game of hide and seek. Arthur sends the knights, the guards, and the castle servants out on a search, but Arthur is the one who ends up finding him. He’s sleeping by a fire in the kitchens, mouth and hands sticky with the honey candies Gwaine's admitted to plying him with.

"Did I win?" Marlin asks sleepily.

"You won a chance at nap time," Arthur grumbles at him, being gruff to hide his relief. He picks Marlin up and carries him to bed so that Marlin can't run away... and maybe so he can feel the boy's heartbeat. (Losing Merlin's child would have been bad. Arthur's certain Merlin would've blamed him even though it was entirely Gwaine’s fault.)

Apparently the sugar high from the candy has worn off, because Marlin sleeps for several hours once Arthur tucks him in.

*****

Once he wakes up, Arthur decides he should do something quiet and much less exciting than getting lost and being the subject of a city-wide search. So, Arthur teaches Marlin to play chess. He is surprisingly cunning. To be perfectly honest, although he would never admit it out loud, Arthur knows he probably gets his cleverness from Merlin. He’s still surprised and impressed by the intelligence Marlin shows at such a young age. Marlin isn't good enough to beat him yet, but he's clever and Arthur can't help but feel proud.

He realizes, afterwards, that it's ridiculous. What right does _Arthur_ have to feel proud of _Merlin's_ child, a child who already has a home and a loving parent and soon, probably, a doting new father? But...

Arthur _is_ proud of Marlin. He hasn’t even known the child a week and he already loves him. Arthur knows he can be quick to give trust and love, but he thinks he is breaking his own record here. He can't help it, though. Everything about Marlin is Merlin's, too, and so just like his father, Arthur loves the child with a startling intensity.

Sometimes, Arthur daydreams about having the boy come live in Camelot. Not - not that Arthur wants anything to happen to his mother, because Arthur could never, not even in a daydream, wish that fate on anyone, especially not a child he loves. But Arthur thinks about watching Merlin raise him, thinks about being an uncle or a second father figure to the boy. Thinks about teasing Merlin by offering to train him as a knight, about giving him terribly extravagant gifts at holidays, about teaching him to read and do math, about hugging him and protecting him and giving him everything he could ever want ... it makes Arthur smile, thinking about raising Merlin's child with him, and spoiling the boy rotten.

It isn't particularly that Arthur wants to be a father, in general. He likes children well enough as an abstract idea, and he obviously intends to have an heir someday - and hopefully a larger family. But his longing to keep Marlin is specifically about the boy himself, and his father. It's about the fact that Arthur has a deep, unconditional love for the both of them, and thinking about Marlin leaving feels like he's being punched in the stomach.

 

**day five**

Arthur always spends an afternoon a week sitting on the throne and giving audiences to anyone, noble or common, who wants them. During this week’s audiences, Marlin escapes from his babysitters, Gwen and Gaius, and sneaks into the throne room. Arthur waves Marlin towards him in between audiences. Marlin runs up to the throne (brushing past the legs of an unimpressed guard) and clambers up to sit on the arm of the throne, feet in Arthur’s lap.

"What are you up to?" Arthur asks.

Marlin explains that he's bored and Gaius's leeches are scary.

“Would you like to help me run the kingdom?” Arthur offers.

Marlin agrees, so Arthur lets him beckon the next petitioner to speak to them.

The audiences are much more fun with Marlin there, which makes up for the fact that Marlin makes friends with a goat herder girl from outside the city and Arthur has to give her mother extra money because of it.

*****

Arthur tucks Marlin in at bedtime, because Gaius is too scary to cross. He pulls the blankets up over the boy's shoulders and wishes him a good sleep. But Marlin tugs at Arthur's sleeve before the king can leave.

"What is it, Marlin?" Arthur asks, concerned. Marlin has been quieter than usual all evening, and Arthur's grown worried.

"I want to see my mother," Marlin says.

Arthur's heart pangs. How can he tell Marlin his mother is ill, and he cannot see her for a long time, or perhaps forever? Arthur has too much experience with dying mothers to be the one to break that news to the child.

"She's gone away for a little while," Arthur says instead. "She's sent you here for Gaius to take care of. But she's in very good hands, and you'll see her soon, I'm sure."

Arthur squeezes the boy's shoulder and prepares to leave like he does every night after he says goodnight to Marlin and tucks him into Merlin's bed. But Marlin calls him back.

"Arthur? Don't go yet."

Arthur sits on the edge of Marlin's bed, unable to leave with those eyes trained on him. An exact copy of Merlin's, filled with worry and trust, although a much more childlike and absolute trust than Merlin's in him. Marlin is like a tiny Merlin and Arthur has never wanted to protect anyone this much.

"I'll stay as long as you like," Arthur says.

"Will you tell me about my father?" Marlin asks. "You said his name was Merlin, right?"

Arthur thinks of hearing Merlin wish to know his own father. For Merlin's sake he wishes they'd known about the boy sooner. Merlin would've treated the boy well, been a great father. Marlin should know, Arthur decides, that his father is brilliant and brave and strangely wise and the best friend Arthur's ever had.

"Let's see," he tells Marlin. "Well, first of all, you get these ears from him," he says, tugging on one of Marlin's enormous ears. "You're the spitting image of him really - hair, eyes, exactly. He's also the bravest man I've ever known."

Marlin's smile grows with every passing word.

Arthur tells him the story of the time he and Merlin faced a dragon together. He leaves out all the death and injuries - those shouldn’t be part of a bedtime story - and instead talks about their quest to find the Dragonlord, their failure, and then - quickly, at Marlin’s dismay - their desperate last stand and their final victory. He tells Marlin how Merlin saved his life on the way to find the Dragonlord, and how bravely Merlin stood before a dragon.

He isn't sure exactly when Marlin falls asleep, but he looks up to find Marlin's eyes closed and a sleepy smile on his face.

Arthur lays a kiss on the boy's forehead before sneaking out very quietly.

 

**day 20**

Arthur and Marlin soon fall into a routine. Arthur performs his kingly duties during the mornings and afternoons, while Marlin is taken care of by whoever is available - although no one leaves Gwaine with Marlin unsupervised again. After Arthur is done working, he always spends a few hours playing with Marlin, and he tucks him in every night with a story about Merlin. (Marlin’s favourite, which he’s made Arthur tell him at least five times, is the story of how Merlin and Arthur met. Marlin giggles the whole way through every time.) It’s a nice routine, and Arthur likes it.

Then, almost three weeks after Arthur’s arrival in Camelot, the routine is jarringly broken. They’re in Arthur’s chambers, playing with Marlin’s favourite toys, the fort and wooden soldiers and king and not-evil warlock.

"Gimme the red man!" Marlin yells, reaching for one of the soldiers as he mounts an attack on the evil teddy bear.

Arthur takes the red soldier and holds it over his head, grinning. "What do you say?" he asks, because he has maybe been spoiling Marlin a little _too_ much and he’s recently been trying to instill manners into him. Merlin could be back any day now, Gaius says, and Arthur doesn’t want to be accused of influencing Marlin to turn into a prat.

Marlin pouts. "Give it back!"

"What do you say?" Arthur repeats.

Marlin's tiny hands turn into fists which he props on his hips. He's absolutely adorable. Arthur is laughing at him when his eyes turn gold.

The little toy flies out of Arthur's fingers and into Merlin's hand. Arthur freezes, feeling the smile slide off his face.

"Marlin, did you just use magic?"

"No," the boy denies, eyes still golden.

Arthur isn't sure how this is possible. He thought magic was something you had to train in, something that required incantations and poultices and other evil gimmicks. Not something that a five-year-old could do with ease, and without any thought, or spells, or doing anything at all but glaring at Arthur.

"Marlin," Arthur says, seriously, kneeling in front of the boy. "You can’t _ever_ do that again, understand? Magic is - you aren't allowed to use magic. If _anyone_ saw you, you could be in danger."

Marlin sniffs. "I'm sorry," he says. "I didn't mean it."

"No-" Arthur says, quickly. "It's all right, I'm not mad - but not in front of anyone else, promise?"

"Promise," Marlin says quickly.

Marlin still looks teary and Arthur cannot believe he's doing this, but he draws the little sorcerer into a hug. Rubbing Marlin's tiny back, he promises, "I'm not going to tell anyone."

Arthur is going to tell Merlin. Merlin will need to know his child is a sorcerer. He'll make sure Merlin knows he would _never_ allow Marlin to come to harm because of it. Because of anything. If Merlin wants Marlin to stay in Camelot, Arthur will look into changing the law for his child.

Maybe Gaius should be told as well. Gaius knows about sorcery; he might teach Marlin how to control his powers. Clearly keeping magic secret is bad, as keeping Morgana in the dark ended so badly. They can't let Marlin undergo the same thing.

"Uncle Arthur? Are you going to let go soon?" Marlin says into his shoulder.

Arthur releases him with a ruffle of his hair.

"No magic in front of anyone?" he checks.

"No magic in front of anyone," Marlin agrees.

 

**day 24**

It’s a few days later that Gaius laces Merlin’s breakfast with a potion he’s been working on.

Merlin grows and turns pale and says “Oh _God_.”

“We need to get our stories straight before Arthur gets here,” Gaius says.

Merlin’s reeling from shock. He hadn’t remembered his old life when he was little, but he remembers everything his little self went through. Gaius had told him he’d been sent to visit by his mother, and slept through the journey. He hadn’t explained why Merlin was to answer to “Marlin”, just scowled at him so fiercely that five-year-old Merlin was too cowed to object. And so, Marlin had believed himself a child and played children’s games with everyone, but mostly Arthur, and then he’d _done magic in front of Arthur_.

Merlin is still trying to wrap his head around all this when Arthur comes through the door, casually, because he thinks it is just like every other day.

“Merlin!” Arthur exclaims. “You’re back!”

On one hand, Merlin is incredibly pleased to hear how happy Arthur is to see him, _adult_ him, given that Arthur usually pretends not to care. Arthur must have really missed him. On the other hand - Merlin has to stifle his instinct to run to Arthur and throw his arms around him, which was how Marlin greeted Arthur every day. Merlin can’t imagine how Arthur would react to an adult Merlin doing that, though, so instead he says, “Hello, Arthur.”

"Where's Marlin?" Arthur asks, looking around. He's got a toy sword in one hand, which is completely dwarfing it, Merlin notices now, and Merlin can't bear how sad it is, that this toy is meant for a boy Arthur will never see again.

He's going to tell Arthur _everything_. He opens his mouth -

"He's with his mother, sire," Gaius says. "She's recovered fully."

There's a split second before Arthur covers up his crestfallen look, and it wounds Merlin horribly. Then Arthur nods and says, "Good, I'm glad," and Merlin has never felt so awful.

Merlin is already aching, a little, because the unconditional love Arthur gave Marlin has been taken away from him. How must Arthur feel, knowing he may never see Marlin again?

 

**after**

Arthur mopes.

Merlin thinks maybe he should be offended by how much Arthur misses his five-year-old self. Which is definitely _more_ than Arthur missed Merlin when Marlin took his place. He’s not, though. Instead, he thinks it's adorable, and he's touched that Arthur got so attached to his "son".

So Merlin isn't hurt because he's jealous when Arthur picks up Marlin's toys and sighs, or when Arthur looks disappointed to see an adult attached to Merlin's ears. He's hurt because Arthur's hurting. And it's worse because Merlin feels guilty. This wouldn't be happening if Merlin was a competent sorcerer. Or if he were an honest friend.

*****

“Will Marlin be coming for a visit again anytime soon?” Arthur asks, about a month after Marlin has “left”. He’s trying to be casual about it, not even looking at Merlin when he asks, but Merlin knows how much Arthur wants Marlin.

“I don’t think so,” Merlin says. “I’m sorry, his mother wants him to stay there.”

“Oh,” Arthur says quietly.

Merlin keeps tidying Arthur’s chambers, thinking that will be the end of it, and then Arthur says, “Merlin?”

“Yes, sire?”

“If that’s really why you aren’t bringing Marlin to Camelot, that’s your business, but you should know you don’t need to keep him away for his safety.”

“...what do you mean?” Merlin asks, because _he’s_ not going to be the one to bring up what he thinks Arthur is trying to bring up.

“Marlin told me he’s a sorcerer,” Arthur says quietly. “I won’t hurt your son, Merlin. You needn’t be afraid of bringing him to Camelot.”

Merlin has never been more astonished in his entire life.

“I’m looking into changing the laws,” Arthur says. “I didn’t know, before, that a child so young could have magic - he doesn’t even know what he’s doing, it isn’t fair to punish him or others like him.”

“You’d do that for me?” Merlin whispers.

“It’s the right thing to do,” Arthur says, looking away again, because he’s lying: he is doing this, at least partially, for them.

“I’ve also been thinking,” Arthur continues. “You could bring him to talk to Gaius. Gaius was a sorcerer, too, remember, and it might be good if they talked about it. I don’t want him to feel like Morgana did - alone and scared.”

Merlin honestly feels like he might cry. Arthur cares so much about Marlin - about <em>him</em>.

“Thank you so much, Arthur,” Merlin says. “I’ll - I’ll see if I can bring him to visit.”

*****

When Merlin finds Arthur actually playing with Marlin's toy soldiers, making the king and the sorcerer fight side by side, he decides that enough is enough. He starts brewing the potion again that night.

*****

Arthur bursts into Gaius' tower to find Merlin. He finds a big-eared boy, all right, but he's about 15 years too young.

"Marlin!" Arthur exclaims. He sweeps across the room, grabs Marlin, and encloses the boy in a huge bear hug.

"Uncle Arthur!" Marlin throws his arms around Arthur's neck and squeezes. Arthur doesn't even care that Marlin's trying to strangle him.

"Where's your dad?" Arthur asks, drawing back from the hug.

"Dunno," Marlin says. "Can we play with the toy soldiers? And can we get the honey cakes from Cook? And can we -"

Arthur has so much work to do today. He has reports to go over, audiences to hear, knights to train, and accused criminals to judge. But...

"Absolutely," he says. He sets Marlin down. "Come on, I'll race you to my chambers."

(Arthur lets him win.)

*****  
Most of Marlin’s toys have been put away, but the toy soldiers are still out, because Arthur is a masochist. He’s glad of that decision now.

They fall back into their routine quickly enough, although Arthur treasures every moment more now that he knows when Marlin will be leaving - Gaius says he has to be sent back to his mother at the end of the week. He teaches Marlin how to use the tiny wooden sword he had made for him, manages to laugh when Marlin makes butterflies in his chambers, and tells Marlin a different bedtime story every night.

Well, that last one he stops doing when he tells Marlin about the Dorocha and the next morning he finds Marlin in Gaius’ bed, and Gaius glares at him all day for giving Marlin nightmares. Then Arthur goes back to the stories Marlin already knows and loves.

*****

Marlin has decided he likes to "help" Arthur run his audiences with the nobles and commoners that come to see him and line up to talk to him. Honestly, having a small child around seems to improve everyone's manners, especially the nobles who come in with their rivals, each demanding Arthur to be entirely on their side. So on audience day, Arthur dresses Marlin in the little suit that he used to wear when he was small and his father let him come to important events. In the throne room, Marlin runs up the dais to the throne ahead of him, and Arthur laughs even as the guards and nobles look uncomfortable at this breach of etiquette by the small boy. Marlin is clearly too full of energy to be trusted to stay still on his own, though, so Arthur picks Marlin up and settles him on his lap when he sits on his throne.

The first audience is a woman seeking healing for her son. Arthur tells her to see Gaius, and Marlin asks how old the son is and then offers the woman a toy soldier he's somehow snuck down from Arthur's room. She takes it and thanks them both for their kindness. Marlin beams up at Arthur like this is the best thing that's ever happened to him.

The second audience is one of Arthur's lords accusing another one of screwing his wife. Normally, Arthur would be unimpressed by this. The thing is though that the lords keep glancing at Marlin and they won't say anything inappropriate in front of the boy. So it takes ten full minutes before Arthur understands what the complaint even is, and then it's all he can do to not laugh at their euphemisms for the next ten. He comes up with a solution for them, which is fair and just and euphemistically presented, and they bow and leave. Marlin giggles.

The third audience is a glaring old man who raises his hand and shouts a word and brings stones crashing out of the walls around them. Marlin screams and his eyes flash gold and the huge boulder that was falling towards Arthur's head is re-directed and goes flying at the sorcerer instead.

The sorcerer falls, and that ends the original spell, but the damage has already been done. Almost everyone in the room has fallen, bleeding or bruised or unconscious or possibly dead already. The throne room is destroyed, the table smashed and ruined. Worse still, the stones in the walls have been loosened by the original falling rocks, and there are still loose rocks flying everywhere.

A couple hit Marlin before Arthur can shield him, one hitting him in the head and the other in the leg. The little boy's eyes roll up in his head and he collapses, barely giving Arthur time to catch him. _Merlin's going to kill me,_ Arthur thinks, as he pulls the boy tightly against his chest and leans over him to protect him from any further debris.

And then he feels the body he's holding start...growing.

*****

Guards throw open the throne room doors and rush in. They run to the people scattered on the floor, lifting stones off the injured and helping them to stand. The room is already filled with moans and cries of pain; now the guards’ stomping and shouting of orders joins the chaos.

Merlin is in the center of it all, but he feels strangely removed from it. His heart is beating out of his chest and he tunes out the noise around him, listening desperately for Arthur’s reaction.

Merlin would normally try to sell Arthur some sort of story. Somehow convince him that Merlin had not, in fact, just transformed from a five-year-old boy into a full-grown man, but had instead very quickly switched places with Marlin. However, given that Arthur had been literally holding onto him throughout the entire transformation, he felt that excuse was unlikely to hold much water.

"Marlin?" Arthur asks, and okay, maybe Merlin can salvage this.

But then Arthur looks into Merlin's face, and Merlin can't hide his trepidation, his _fear_ , at what Arthur might do and how he might react. Something that Marlin, full of trust and admiration and uncomplicated love, would never feel when faced with Arthur.

"Merlin," Arthur states.

Merlin usually loves the way Arthur says his name, teasingly or exasperatedly or exhaustedly or admiringly (if he thinks Merlin isn't listening) but most importantly almost always affectionately. But he could've done without ever hearing Arthur say his name in this particular tone. So hurt and disappointed, even though he hardly sounds surprised.

"I'm sorry," Merlin whispers. "I wanted to tell you."

Arthur's humourless laughter _hurts_. "Wanted to tell me you've been a sorcerer as long as I've known you? Or wanted to tell me the child I thought was your son was just _you_ in disguise?"

"Mostly the sorcerer part?" Merlin says weakly. "But, it wasn't like that, Arthur. Marlin wasn't me in disguise, exactly - he was an accident at first. I didn't _mean_ to turn myself into a child, and I lost all my memories of you, but you were _so nice_ \- and you missed Marlin so much, I just wanted you to see him again. I didn't know how to tell you any of it, Arthur, I'm so sorry."

Merlin has been avoiding Arthur's gaze but now he finally looks into the king's eyes. "I'm so sorry," he repeats.

Arthur sighs, then - roughly, like he doesn't really care, the callous affection he always shows adult Merlin - he puts his hand on the back of Merlin's head and pulls him into what could be called a hug. A horrible, one-handed (let alone one-armed) hug that's mostly him mashing Merlin's face into his chest, but a hug nonetheless. Merlin squirms and beats on him, because this is rather uncomfortable, and he lets go.

"I'm sorry too," Arthur mumbles. "I'm sorry you felt you couldn't tell me. And that, y'know, I technically ought to execute you."

"You won't," Merlin says.

"I might," Arthur grumbles back.

"You'd never hurt Marlin," Merlin says.

Arthur snorts and allows that, but then he puts an arm around Merlin properly and says into his ear, "I'd never hurt you, either, Merlin, and you'd better know that by now."

Merlin just grins up at him.

"This explains so much about why I've never seen you and Marlin in the same room," Arthur says. "I didn't think you'd be a neglectful father."

"I'd be a great father," Merlin says. "I'd never tell my child horrifying ghost stories before bedtime."

"That was _one time_ ," Arthur insists.

"It only takes once for a lifetime of nightmares!" Merlin argues.

"Aw," Arthur mocks. "You can still crawl into bed with me if you like."

Merlin hits him, which obviously hurts Merlin's hand far worse than Arthur's shoulder.

"Treason," Arthur grumbles. Then clarifies, "I'm talking about the hitting the king part. Not the sorcery part, or - have you committed any other crimes I should be aware of?"

"Er," Merlin tries a smile. "If you haven't noticed, let's go with... no?"

Arthur snorts, then grabs Merlin by the arm and pulls them both to their feet. They start making their way out of the decimated hall, past rubble and bodies and smoking candles and smashed food. Merlin's limping, one ankle hurt in his stumbling to protect Arthur. The king lets the sorcerer lean on him, supporting his weight as they walk.

 

**epilogue**

"Merlin," Arthur says.

"Yes," Merlin prompts.

"I don't suppose - that is - " Arthur starts over. "Marlin was... very special to me, as you know, but I always sort of wanted to ... raise him with you, you know?"

Merlin gapes at him; Arthur carries on unhindered.

"I'm just saying, that it would be nice. Someday."

"Are you talking about our future children before you've even _kissed_ me?" Merlin teases.

"If you're objecting, then I can do something about that," Arthur says. He takes Merlin's arms in his hands, turns Merlin to face him, and pauses, reading Merlin’s face for permission.

Merlin darts in and smashes his lips against his king's.

When he finally draws back, he says, "Fine, but Gaius isn't naming our child."

"Well, you aren't either," Arthur retorts. "Dragoon, honestly?"

Merlin sniffs. "I was under pressure.”

**Author's Note:**

> warning: this is not in any way related to my other fic "Uncle Merlin", and you should not read that if you are looking for continued fluff!


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